The antibacterial activities of 3 plant extracts of were studied. The dried extracts of Salvia officinalis (Lamiaceaea) (leaf) and Opuntia  ficus  indica (Cactaceae) (fruit) were tested in vitro against 3 bacterial species named, Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa  by disk diffusion and micro-dilution. The patterns of inhibition varied with the plant extract and the organism tested. Staphylococcus aureus and Escherichia coli were the most inhibited microorganisms. Salvia officinalis extract was the most active against Pseudomonas aeruginosa. Results of this kind herald the interesting promise of designing a potentially active antibacterial agent of plant origin. It  can  be suggested that ethanol extracts of these plants are a great potential source of antibacterial compounds that could be used in the formulation of new antimicrobial drugs of  natural  basis.